This invention relates to a telemetry device for transmission of information in a liquid medium by generation of pressure pulses, especially for transmission of measured data from a well to the earth's surface during drilling, with a signal transmitter, which is installable in a conduit through which the liquid medium flows, and which has a stator that partly blocks the conduit and has at least one passage through which medium is passed from a side located upstream from the stator to a side located downstream from the stator. The device includes a rotor that can rotate in the conduit, that is adjacent to the stator and that has at least one opening and that, by means of the rotary movement, can be moved either into a throttling position in which the rotor throttles the flow of liquid medium through the passage in the stator or into a passing position in which the opening of the rotor permits a substantially unthrottled flow of liquid medium through the passage in the stator. By repeated movement of the rotor from the passing position into the throttling position and back into the passing position at controlled intervals, there can be generated a coded series of pressure pulses, which are transmitted by the liquid medium to a remote location and are picked up there by a receiver.
Telemetry devices of this type are employed in particular in directional drilling in order to transmit measured results determined underground during drilling, from logging instruments disposed in the drill string to the surface and, on the basis of these measured results, to permit influencing the progress of drilling to the desired extent.
Known applications for such telemetry devices are described in U.S. Pat. Nos. 3,309,656, 3,764,968, 3,764,969, 3,770,006 and 3,982,224. The telemetry devices in these cases are part of well-logging instruments for making measurements during drilling, which instruments are installed in the lower end of the drill string close to the bit and which transmit measured data in the form of pressure pulses through the drilling fluid to a receiver at the surface. The pressure pulses in these cases are generated by the rotor which is driven continuously in rotation by an electric motor, the angular velocity of the rotor being varied in order to change the pulse frequency, according to the data to be transmitted, by means of special mechanisms which are electrically activatable. These known instruments have proved to be large, laborious and expensive. Furthermore they need extensive and expensive energy systems and mechanisms in order to operate the telemetry devices, and so either large and expensive battery packs or turbine-driven generators are needed for entry generation. Furthermore the known instruments are installed permanently in the drill string and cannot be removed without dismantling the drill string.
From U.S. Pat. No. 4,914,637 there is known a well-logging instrument with a telemetry device of the type mentioned initially in which the rotor is disposed in the flow of drilling fluid and has blades that are impinged upon by the drilling-fluid flow, whereby a continuous torque acts on the rotor and in each case turns the rotor further in increments from one position to the next when a blocking device is released by which the rotor can be locked in a throttling position or a passing position. By virtue of this direct drive of the rotor by means of the drilling-fluid flow the demand for electrical energy is reduced in this known instrument, but the disadvantage nevertheless exists that the torque acting on the rotor varies depending on the position of the rotor, and so the blocking device is sometimes exposed to very large forces and is subject to relatively severe wear. Furthermore the torque of the rotor is strongly dependent on the hydraulic conditions of the drilling fluid, and so torque fluctuations can occur that interfere with signal generation and thus affect information transmission.